The performance requirements of semiconductor devices are ever increasing. An important performance requirement of many semiconductor devices is power consumption. Power consumption traditionally rises with increases in semiconductor device complexity and speed.
Traditional plastic packaged semiconductor devices do not include a heat sink. The lack of a heat sink becomes a problem as device power requirements approach one and one half to two watts. Increased semiconductor device power consumption translates into increased semiconductor device operating temperatures. Heat generated by a semiconductor device migrates through the plastic packaging material which can reach temperatures of 100.degree. to 120.degree. C. Sustained high operating temperatures can result in outright semiconductor device failure or the plastic package may begin a process of decomposition resulting in package cracking and eventual device failure.
Traditional methods for removing excess semiconductor device heat include liquid cooling, forced air cooling, the incorporation of a heat sink inside the plastic package, or a combination of these methods. Liquid cooling is expensive to implement and operate. Forced air cooling usually requires an electric fan and electricity to run it. Incorporation of a heat sink inside a plastic package to disperse heat away from a semiconductor device is the most commonly utilized heat dispersion option.
Two methods are currently used to incorporate a heat sink into a plastic packaged semiconductor device. The first method involves dropping a heat sink into a plastic mold prior to device molding. The second method involves attaching a heat sink to a leadframe using double sided tape. Both methods require a lead frame 10 having lead fingers 12, as shown in FIG. 1. In the first method (not shown), an insulating film is applied to areas of a heat sink that will contact the lead fingers. In the second method, a double sided tape 14 is used to connect a heat sink 16 to lead fingers 12, as shown in FIG. 2. FIG. 3 is a side sectional view of the device of FIG. 2. FIG. 4 is a bottom view of the device of FIG. 2. FIG. 5 is a side sectional view of the device of FIG. 4.
A disadvantage of the first method is yield losses resulting from heat sink misalignment. A disadvantage of the second method is the additional cost of the double sided tape and the time and labor required to properly attach a metal heat sink to a lead frame using the double sided tape. What is needed is a more cost efficient way of incorporating a heat sink into a packaged device.